The mechanism of extracellular materials in tissue interaction and chondrogenic differentiation has been studied for the past 20 years. In the last five years we have developed a number of microanalytical assays to identify 1. biochemical changes in somite chondrogenesis, 2. the nature of perinotochordal materials and their influence on somite chondrogenesis, 3. the effect of inhibiting the synthesis of specific perinotochordal materials on somite chondrogenesis. Although perinotochordal material induces somite chondrogenesis, there are gaps in the knowledge of the exact nature of the material involved in such induction. Whether alterations in the perinotochordal material synthesis affect somite chondrogenesis has not been investigated. Information regarding yet another perinotochordal component, fibronectin, and its role in somitogenesis and chondrogenic differentiation is fragmentary. Even though somitic and lateral plate mesoderm (from which limb outgrows) arise from common origin, we are completely ignorant about the somitic macromolecular materials influence on limb development. The research proposed seeks to 1. characterize one of the perinotochordal materials', the proteoglycans, 2. analyse inductive role of various proteoglycan components obtained from chick embryonic sternum (such as PG monomers, core protein, hyaluronic acid, link protein and chondroitin and keratan sulfate rich peptides) on somitic chondrogenesis, 3. study the effect of metabolic inhibitors (in vitro) on the synthesis of perinotochordal proteoglycans and the inductive cpacity of such treated notochord and the proteoglycan isolated on somite chondrogenesis, 4. study the expression in somite differentiation of the synthesis of cartilage specific proteoglycans, link proteins, hyaluronic acid binding regions, 5. identify the macromolecular contribution from the somites in limb differentiation, and 6. study the distribution and sequence of the appearance of fibronectin and cartilage specific proteoglycans in somite differentiation. These studies will be made by 1. inducing somite chondrogenesis, using proteoglycan isolated from notochords cultured in vitro, 2. growing somites and notochords under various experimental conditions. Chondrogenesis will be judged by the synthesis of cartilage specific large proteoglycan synthesis and other chemical composition.